OF-3031: LocalSession isClosed 'old' implementation through configuration
The change made to `LocalSession#isClosed()` under OF-3031 seems to be the 'correct' change, but this change is likely to introduce issues with code that depends on the old behavior.
To allow for backwards compatibility, this commit introduces a configuration property `xmpp.session.isclose.connectionbased` that can be used to restore the old behavior. By default, the old behavior will be disabled, but this can be changed by changing the value of this property to `true`.
OF-3031: Session's 'close' state no longer based on its backing connection
In the early days, a Session was always backed by a (socket) connection. When the connection was closed, so was the session, and vice versa.
With Stream Management, this no longer is the case. A session can remain unclosed (detached) while its connection is closed.
This commit changes the behavior of `LocalSession#isClosed()` to be based on the session's `status` field, and no longer on the connection's connectivity state.
OF-3029: Prevent false warnings about data inconsistency
It appears that this warning is also logged (incorrectly) in a scenario where user has a session that relates to a different route (in other words: when the user is using more than one device / the addressing uses different resource-parts in their JIDs). Openfire should not be logging that warning in such cases.
